全文获取类型
收费全文 | 411篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 19篇 |
地球物理 | 65篇 |
地质学 | 141篇 |
海洋学 | 69篇 |
天文学 | 82篇 |
综合类 | 1篇 |
自然地理 | 30篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 22篇 |
2012年 | 27篇 |
2011年 | 18篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 26篇 |
2007年 | 23篇 |
2006年 | 28篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 20篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1956年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有424条查询结果,搜索用时 109 毫秒
421.
Jens Wittsten Fredrik Andersson Johan Robertsson Lasse Amundsen 《Geophysical Prospecting》2019,67(6):1486-1497
A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test. 相似文献
422.
In this paper, a time series from 1999 to 2007 of absolute total electron content (TEC) values has been computed and analyzed
using singular value decomposition (SVD). The data set has been computed using a Kalman Filter and is based on dual frequency
GPS data from three reference stations in Denmark located in the midlatitude region. The station separation between the three
stations is 132–208 km (the time series of the TEC can be freely downloaded at ). For each year, a SVD has been performed on the TEC time series in order to identify the three time varying (daily, yearly,
and 11 yearly) characteristics of the ionosphere. The applied SVD analysis provides a new method for separating the daily
from the yearly components. The first singular value is very dominant (approximately six times larger than the second singular
value), and this singular value corresponds clearly to the variation of the daily cycle over the year. The second singular
value corresponds to variations of the width of the daily peak over the year, and the third singular value shows a clear yearly
variation of the daily signal with peaks around the equinoxes. The singular values for each year show a very strong correlation
with the sunspot number for all the singular values. The correlation coefficients for the first 5 sets of singular values
are all above 0.96. Based on the SVD analysis yearly models of the TEC in the ionosphere can be recomposed and illustrate
the three time varying characteristics of the ionosphere very clearly. By prediction of the yearly mean sunspot number, future
yearly models can also be predicted. These can serve as a priori information for a real time space weather service providing
information of the current status of the ionosphere. They will improve the Kalman filter processing making it more robust,
but can also be used as starting values in the initialization phase in case of gaps in the data stream. Furthermore, the models
can be used to detect variations from the normal local ionospheric activity. 相似文献
423.
Nils Andersson 《Journal of Astrophysics and Astronomy》2017,38(3):58
Neutron stars involve extreme physics which is difficult (perhaps impossible) to explore in laboratory experiments. We have to turn to astrophysical observations, and try to extract information from the entire range of the electromagnetic spectrum. In addition, neutron stars may radiate gravitational waves through a range of scenarios. This brief summary outlines some of the main ideas, focussing on what we do and do not know, and the challenges involved in trying to catch these faint whispers from the very edge of physics are described. 相似文献
424.
W.M. Irvine Z. Abraham M. AHearn W. Altenhoff Ch. Andersson J. Bally W. Batrla A. Baudry D. Bockelée-Morvan G. Chin J. Crovisier I. de Pater D. Despois L. Ekelund E. Gerard T. Hasegawa C. Heiles J.M. Hollis A. Wootten 《Icarus》1984,60(1):215-220
Detections and upper limits to the continuum emission (1 ≤ λ ≤6 cm) and spectral line emission (OH, CO, CS, HCN, HCO+, CN, CH3CN, CH3C2H, NH3, H2O, HC3N, CH3CH2CN) are reported from radio observations of Comets 1983d and 1983e. Comparison is made with observations of CN at optical wavelengths. These results may be useful in planning future cometary observations. 相似文献